Windows Defender Does Not Start in Windows 10

Windows Defender is the default anti-malware solution that Microsoft integrates with Windows. Many people choose to not use Windows Defender and choose to use for example ESET, Bitdefender or any other anti-malware solution. However, for normal computer users Windows Defender should be more than enough. But what if Windows Defender fails to start? What can you do to start Windows Defender? In this article we are going to show you a couple of ways to check if all settings are set correctly and that you don’t perhaps miss some important services, registry entries or files on your system.

This article is split up into different steps. We suggest you follow it step by step till once step solves your issue. If you were instructed to use a specific step, then ignore the rest.

Step 1: Reboot your system

It might sound stupid but many problems with Windows Defender simply comes from a service not running, for example it crashed. By rebooting your system, you will restart all services that are needed again. If you tried this before then please continue to the next step. If this solution did not work then please also continue to the next step.

Step 2: Make sure no other services are causing issues

There could also be a service running which is causing these problems with Windows Defender, to make sure that’s not the case we will boot your system clean. This means that we only boot Windows with the only absolutely necessary services and programs. To see how you boot your system clean please read: How to Boot Windows 10 Clean?

If a clean boot did not help, then please continue to the next step. If clean boot did help, then once again use the guide above and start enabling Services again one by one or in small groups till you find the service that is causing the issue.

If you have any 3th party anti-malware, anti-virus and anti-spyware software installed then please completely remove these programs from your system by using the uninstallers provided by the publisher. If you cannot find the uninstaller then please use the list below to find the uninstaller for the software you are using, or the steps you should take to remove these programs.

If your software is not in the list above, then please use google to find the removal tool for your program. You could use this search perimeter for example. [PROGRAM NAME] removal tool.

Once your 3th party application has been removed, reboot your computer and try to use Windows Defender again. If the program still does not work, then continue to the next step.

Step 4: Are you perhaps infected with malware?

A common reason for Windows Defender for not working is cause of an already present malware infection on your system which is blocking Windows Defender from starting. It’s` important to scan your system as soon as possible to determine if you’re already infected and your files or personal information might have been compromised. There are different kind of tools that can do this. Please use the two listed below first and see if they help.

Look for any entry to MSASCui.exe, MpCmdRun.exe or MsMpEng.exe. If you find these then right-click them and choose Delete

If you do not find any entries at step 4 then no worries, that’s normal then this step is completed for you and you should continue to the next step. If you did find entries and deleted them then close Registry Editor and reboot your system. Once your system is rebooted check and see if Windows Defender now works. If not then continue to the next step.

Step 6: System File Checker Scan

You might have damaged files on your system which are causing the problems your experiencing with Windows Defender. To make sure you do not have any damaged files or to attempt to fix them please run an SFC (System File Checker) scan.

Open Elevated Command Prompt by following one of two methods:

Press the Windows + X at the same time, then choose Command Prompt (admin)

Type the following command “sfc /scannow” and hit enter

Wait for the results to come back.

If System File Checker found damaged files and was able to fix them then try to use Windows Defender again after you rebooted your device. If Windows Defender still does not work or SFC did not find any problems, then continue to the next step.

Perhaps Windows Defender is disabled though the registry or the key is simply missing. We should check this.

Press the Windows and R key at the same time. This will open a Run window.

In the Run dialog type regedit and then hit enter or Run

In Registry Editor navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender. By unfolding each folder step by step.

Check if there is a DWORD DisableAntiSpyware

If there is no DWORD DisableAntiSpyware then right-click an empty location and choose New -> DWORD, enter DisableAntiSpyware and click on Create. Then double-click DisableAntiSpyware and set the value to 0. If there is a DWORD DisableAntiSpyware then check if the value is set to 0 if not set the value to 0.

You’ve reached the end of this article. We hope that one step was able to solve your problem. If there was no step that helped you then no worries, we might still be able to help you personally on our forums. We want to thank you for reading this article and hope it helped.

2014, 2015 & 2016 Microsoft Most Valuable Professional Windows
Yuri specializes in troubleshooting (crash analysis and devices), system resource utilisation and system performance. He is also very interested in Customer Security. Yuri can be found as Windows Community Moderator and Wiki Author on Microsoft Answers and is active on different communities all across the web.

I have been tearing my hair out for hours trying to get Windows Defender running after removing Bitdefender, which I suspect to be the cause of daily lock-ups. I have tried every suggestion I could find and had about given up, but #7 finally seems to have done the trick. Hallelujah!

AVG could not fix my computer.I gave them 4 attempts.
HP unloaded AVG and turned on Windows Defender.
This morning, just like your article states, Window Defender is turned off. I didn’t turn it off. Furthermore, someone was in my computer in the command bar when I turned the computer on. This happened to me once before. Are your technicians (and AVG’s) vetted? Are their actions checked after they “fix” your computer? This is a pretty new computer and I’m still learning the ins and outs of it.
I want to know that when a tech fixes it, they are unable to get back in. I’m hesitant to go back to the same malware/virus provider when I see someone roaming around my computer when I turn it on.
Thank you.

WindowsInstructed has been founded as a Windows solutions website for the most common Windows issues that users are experiencing while using their system. We index many online communities and look for a pattern of problems. When we find a pattern we will ask one of our experts in that expertise to write a Troubleshooting guide for the problem.